This project addresses the development of a quantitative hyperthermia therapy planning protocol. Preliminary experiments show that a distinctive relation exists between the ratio of steady-state temperature rise to SAR and effective tissue thermal conductivity (which accounts for heat loss due to both conduction and blood flow). However, there is no available method for assessing the thermal dissipative mechanisms within the treatment volume. This development effort will focus on improving measurement instrumentation and methodology for application to both ultrasound and microwave hyperthermia delivery systems. The capabilities of the Enhanced Thermal Diffusion Probe will be extended to yield measurements of temperature, thermal conductivity, and SAR at multiple tissue sites within a treatment volume through development of Multi-Sensor and Catheter Sensor probes. "Characteristic heating curves," relating effective thermal conductivity to local tissue heating, will be developed for a range of hyperthermia applicators at the Harvard-MIT Hyperthermia Center and the Dana Farber Cancer Institute. In the clinical setting, these curves, combined with pre-treatment measurements of effective thermal conductivity, can predict the ability to achieve therapeutic heating, or whether excessive heating of intervening tissues is likely to be treatment- limiting. This will be of immediate benefit to hyperthermia therapy: a standard measure of tissue thermal clearance will enable objective comparison and evaluation of applicators and modalities; the spatial distribution of effective thermal conductivity can be used as a quantitative basis for tailoring the SAR distribution to the tumor; and clearly untreatable regions can be identified to provide the rationale for canceling therapy, for a change of applicator or modality, or for subsequent treatment with a more appropriate applicator.